Operation of gas turbine engines and fuel compositions for use in said engines



United States Patent F 2,993,336 OPERATION OF GAS TURBINE ENGINES AND gUEL COMPOSITIONS FOR USE IN SAID EN- Kenneth John Mackenzie, Eric Lewis Howe, and Richard Thomas Roles, all of Sunbury-on-Thames, England, assignors to The British Petroleum Company Limited, London, England, a joint-stock corporation of Great Britain No Drawing. Filed Sept. 3, 1958, Ser. No. 758,668 Claims priority, application Great Britain Sept. 6, 1957 7 Claims. (Cl. 60 35.6) I

This invention relates to a method for preventing or reducing the deterioration of a gas turbine engine, operating on a mineral oil residual fuel, particularly a petroleum residual 'fuel. This invention also relates to an improved fuel composition for use in gas turbine engines.

It is known that a gas turbine engine, operating on residual fuels containing mineral components, frequently deteriorates in condition and performance due to the accumulation of deposits within the engine, notably upon stator and rotor blades. In general, these deposits comprise sodium-containing compounds and vanadium-com t-aining compounds. Furthermore it has been found that the lay-down of deposits is accompanied by corrosion of the underlying metal surfaces and thus removal of the deposits from the engine fails to restore completely the efiiciency of said engine.

It has been stated that the class consisting of complex aluminium silicates provides suitable additives for residual fuel oils to provide fuel compositions for use in gas turbine engines; within this class of -additive,i felspar has been specifically proposed. We have found that within this broad class of additives consisting of complex aluminium silicates, specific compounds vary considerably in performance. In relation to a residual fuel which has 2,993,336 Patented July 25, 1961 ice residual fuel derived from petroleum and, in powder form, a minor proportion of a metal aluminium silicate complex having a mica crystalline structure. For brevity, said complex is hereinafter referred to as mica.

Residual fuels employed in the compositions of this invention have a small content of vanadium which, under the conditions existing in a gas turbine engine and in the absence of additives, are converted to corrosive vanadium compounds. We have found that using a fuel composition containing mica, the proportion of vanadium in combined form, in the deposits formed on the turbine blades is very small.

The preferred micas are muscovite (potassium mica) and phlogopite (magnesium mica); other micas which may be employed are:

Paragonite (sodium mica) Lepidolite (lithium mica) Zinnwalidite (lithium-iron mica) Biotite (magnesium-iron mica) Lepidomelane (iron micas containing ferric iron in large quantities) The .mica will normally be incorporated, in the fuel, in finely divided form whereby a. suspension is formed. Clearly the stability of the suspension will depend, among other factors, upon particle size, and preferably stirring means will be provided to maintain the composition. 1

According to a further aspectof the present invention there is provided a method of operating a gas turbine. engine upon a residual fuel, of petroleum origin, contain ing vanadium, by which damage or decline in efficiency during the operation of the engine on said fuel, a mica,

' in powder form, is introduced, continuously or intermit not been treated with additive, the resulting fuel compositions will in some cases give an increased rate of buildup of deposits and in some cases may lead to a reduction is considered that a factor of much greater importance is the rate of corrosion of the internal surfaces of the tur-. bine, notably corrosion of rotor blades, since damage by corrosion cannot be remedied during routine overhaul and constitutes a serious limitation on efiective engine life. We have" found that "within the broad class of complex aluminium silicates there is a sub-class of compounds which may be used as additives for residual fuels to provide improved fuel compositions. The improved compositions, when used in gas turbine engines, give a reduced rate of corrosion of internal surfaces of the turbine in comparison with the untreated fuel and also in comparison with compositions derived by the use of additives which, while being complex aluminium silicates, do not lie within the sub-class of compounds in'accordance with the invention. It is an objectof this'invention to provide an improved fuel composition for use. in gas turbine engines. lt fis another objectiof thisiny'ention to provide an improved metho d' of opei atinga gas turbine engine upon a residual fuel, of. petroleum origin, containing vanadium. Other objects will appear hereinafter. f

. .Accordingtothe, presentinvention-there provided a fuel composition, suitable for use in gas turbine engines: containing a major proportion of a vanadium containing tently, into the combustion chamber of said engine.

The optimum rate of feed of mica to the engine depend upon both the rate of feed of the fuel and upon the proportion of vanadium contained in the fuel. In general the use of mica in an amount constituting from 0.1 %=to 1.0% by weight of the fuel will be satisfactory; however the use of greater or smaller amounts also lies within the scope of this invention. When mica is added intermittently, greater amounts will usually be added during the period of injection but normally the amount so addedfwhen averaged, over the injection cycle will not exceed 3% by weight of the fuel fed during this period. The mica may be introduced into the engine by any desired method, including: a v

(a) Direct feed to the combustion zone by screw conveyor I V (b) Introduction as a suspension in the fuel supply via the fuel injection nozzles (0) Introduction as a suspension in bleed oif stream of the main fuel via subsidiary injection nozzles r 1 (d) Introduction as a suspension in a liquidvehicle via subsidiary injection nozzles (e) Introduction in fluidised state into (i) the total air stream to the combustion chamber, or (ii) the air stream to the primary zone that is, the zone, containing As hereinbefore stated, the additive may be introduced into the engine in intermittent manner. Preferably the mica will be introduced over a period of hours by one or other of the methods described and thereafter a substantial measure of protection from corrosion will be achieved notwithstanding that residual fuel free of corrosion preventing additive is employed. After a period of hours of operation under these conditions the cycle will be repeated. i t V Preferably in a cycle of operations the mica is introduced for a period not exceeding 20 hours and thereafter the engine is operated without introduction of mica for a period of at least 80 hours. By way of illustration the cycle may consist of 12 hours operation with injection of mica at the rate of (ll-1.0% by weight of the residual fuel followed by 88 hours operation using residual fuel without mica injection to the engine.

By intermittent injection of mica, as described, the rate of build-up of deposits (during the operational cycle) will be less than is the case when the same amount of mica is continuously injected? nevertheless .good resistance to corrosion will be achieved.

This invention is illustrated but in no way limited by the following example.

An experimental gas turbine combustion rig was employed to test a series of fuel compositions. The combustion rig was of the following construction:

(a) A compressor providing up to 2 pounds of air per second at 3-4 p.s.i.g.

"(b) A pre-hea'ting combustion chamber to raise the air temperature to 350 C.

(c)"The main residualoil burning combustion chamber- (d) A test blade section consisting of four turbine stator blades arranged to simulate the first row of turbine blading.

"(2') Instrumentation, fuel systems and general auxiliaries. i

To simulate the air temperature conditions of an ingas stream and the weight of deposit found by difference. To measure corrosion, the test blades were descaled in the following manner:

The blades were immersed in a boiling mixture of 30 percent weight caustic soda, 2 percent weight potassium permanganate and 68 percent water for one hour after which they were scrubbed under running water with a brass wire brush. The blades were then replaced in the mixture for a second hour and the scrubbing treatment repeated. Water vaporisation losses from the mixture were made good by topping up with distilled water. After the second scrubbing treatment the blades were replaced for two minutes in a mixture of 1 part concentrated nitric acid and 3 parts water to which had been added 1 percent volume of volume hydrogen peroxide. The temperature of this mixture was maintained at '60 C. On removal the blades were Washed under running water, then in acetone and dried ready for weighing.

EXAMPLE 1 Tests 1 and 2 are provided by way of comparison. In test 1, the fuel employed was a kerosine distillate fraction of petroleum origin. In test 2 and test 3 the fuel employed was an Admiralty Reference Fuel, having the code name Mothball, of the following characteristics:

Viscosity (Redwood No. 1 at 100 F.) secs 635 Ash percent 0.058 Vanadium content "ppm..- 258 Sodium content p.p.m 1

In test 3 mica was injected into the total air supply to the combustion chamber. The mica used was muscovite (potassium aluminium silicate complex) and had a particle size such that 80% passed through a 200 British Standard mesh. 7

Test conditions and results obtained are shown in the dustrial gas turbine engine, in which compressed air 40 following Table 1.

TABLE 1 Average 7 Blade Blade gas tem- Additive Injee- Weight In- Weight I Test Fuel Test Durperature at tion Material crease dur- Metal loss No. ation, Hr. entry to and Flow g (corrotest blades, (fouling) sion) mg.

1 Ker0sine 12 650 Nil 1.4 51.0 2 MothbalL- 12 650 N1] 51. 0 144.0 'do 12 650 Mica 0.3% on 220.0 72.0

fuel flow.

would be preheated by a heat exchanger there was pro- Example 2 vided a preheating chamber through which 'the flow of compressed air passed before reaching the main 'combustion chamber; the preheating "chamber was in the.

form of a refractory lined combustion chamber and-was equipped with a medium air pressure atomizing nozzle, operating on keros'in'e. J

A jig, hereinafter referred to as the test'bl'ade holder, and constructed to locate four turbine blades in therelative positions in which they' would be mounted in a paratus described in Example 1.

" were made of the increase in weight (fouling) of the during operation of ;-a turbine) over the two inner blades.

The blade'holder was brought into position for test urposes after steady operating conditionsfhad been,estab lished. To measure fouling; the inner blade s w s weighed both before and after exposurejto-the' exhaust test-blades and of the weight of theblades aftercleaning. Results are expressed as (a) percentage difference (increase or decrease) in fouling, in relation to fouling obtained using fuel Without additive and (b) percentage reduction in corrosion (loss of weight of; the blades after cleaning) in relation to corrosion obtained; using fuel withoutadditive. a The referen cefuel was thefuel knownas Admiralty Reference Fuel "Vanilla which has an ash content of 0.08% by weight, a vanadium content of 360 parts per million and a viscosity (Redwood No; 1 at 100 F.) .of 650 seconds.

In, all the vruns the test blade temperaturewasheld at o9;. C' w 1' T, 1"" V l of said engine and constitutes 0.l-3% by weight of the following Table 2. residual fuel.

TABLE 2 Percentage Test Percentage Dlfler- Reduction Test No. Dura- Additive Injection Position and Rate ence in fouling (by in corrotion, Hr. welght) sion (by weight) 321 12 Muscovite Mica Into High Pressure Fuel 4.0 Increase 23.0

(Slurry in Lub. Pump Suction. 33% by Oil) weight Mica on Fuel Flow. 313 12 Powdered Musco- Primary Zone. .33% by 32.0 Increase 32.0

vite Mica. weight on Fuel Flow. 294 12 .do Primary Zone. 1.70% by 575.0 Increase... 50.

weight on Fuel Flow. 303 100 do Primary Zone. 1.7% by 26.0 Increase 53.0

weight on fuel fiow for first 12 hr. of test only. 319 12 Powdered Phlog- Primary Zone. 33% by 22.0 Reduction 16.

op to ca. weight on fuel flow. B14 12 Powdered Fel- -do 72.0 Reduction Nil spar.

We claim: 6. A method as specified in claim 5 in which the metal 1. A fuel composition, suitable for use in gas turbine engines, containing a major proportion of a vanadium containing residual fuel derived from petroleum and, in powder form, 0.l3% by weight of the residual fuel of a metal aluminium silicate complex having a mica crystalline structure.

2. A fuel composition as specified in claim 1 in which the mica is muscovite.

3. A fuel composition as specified in claim 1 in which the mica is phlogopite.

4. A fuel composition as specified in claim 1 in which the metal aluminium silicate complex constitutes 0.1 to 1.0% by weight of the residual fuel.

5. A method of operating a gas turbine engine upon a residual fuel, of petroleum origin, containing vanadium, wherein damage or decline in efiiciency due to corrosion is avoided or materially reduced wherein, during the operation of the engine on said fuel, metal aluminium silicate complex, having a mica crystalline structure, is introduced, in powder form, into the combustion chamber References Cited in the file of this patent FOREIGN PATENTS 314,443 Switzerland July 31, 1956 315,324 Switzerland Sept. 29, 1956 200,149 Australia Nov. 4, 1955 201,884 Australia May 24, 1956 740,062 Great Britain Nov. 9, 1955 745,012 Great Britain Feb. 15, 1956 762,521 Great Britain Nov. 28, 1956 

1. A FUEL COMPOSITION, SUITABLE FOR USE IN GAS TURBINE ENGINES, CONTAINING A MAJOR PROPORTION OF A VANADIUM CONTAINING RESIDUAL FUEL DERIVED FROM PETROLEUM AND, IN POWDER FORM, 0.1-3% BY WEIGHT OF THE RESIDUAL FUEL OF A METAL ALUMINIUM SILICATE COMPLEX HAVING A MICA CRYSTALLINE STRUCTURE. 